Aerospace and military applications often provide unique challenges to design and manufacturing. Composite lay-up structures are highly beneficial due to their high-strength and reduced weight characteristics. Manufacturing of such structures, however, often pose procedural and other difficulties when applied to large structures. Techniques developed for relatively small structures may become unwieldy and imprecise when applied to the large structures often found in aerospace applications. In order to accommodate these large structures, manufacturers often resort to smaller construction and corresponding assembly of such smaller portions into the desired large structure. This often places undesirable costs and time constraints on manufacturing.
This is especially true in manufacturing of composite structures such as composite fuselage/barrel sections. The mandrels used to lay-up such barrel sections are commonly large rotating structures. Structural stringers are commonly layed-up onto the mandrel and rotated in concert as a composite skin is laid-up on top. Manufacturing concerns arise when the stringers shift or fall out of the mandrel during such rotation. This is unacceptable in manufacturing and poses considerable cost risks to the lay-up procedure.
In response to such concerns, it has become common to place both stringers and mandrel into a vacuum-bag assembly and impose a strong vacuum. In this fashion, the stringers are compressed tightly against the mandrel and may remain in proper position during the subsequent outer skin lay-up. While this may provide a stop-gap approach to stringer shifting, it adds a considerable number of steps which impose time and cost constraints. It does so because the number of stringers that can be positioned in the vacuum bag is limited due to the same shifting or falling concerns as associated with the original lay-up procedures. Therefore, the present solution remains to place only a few stringers on the mandrel, place in a vacuum-bag, impose a vacuum, cut off the vacuum-bag, add more stringers, and repeat the process. Each step of the aforementioned process can frequently only process a limited percentage of the total number of stringers. This slows the manufacturing process down significantly and adds considerable cost.
That is needed is a method and apparatus for securing a greater number of stringers to the mandrel prior to the vacuum-bagging procedure such that the number of vacuum steps could be reduced. Additionally, it would be highly desirable to have a method and apparatus that insured both proper stringer alignment as well as close conformity of the stringers to the mandrel.